This invention relates to a method, and apparatus for performing the method, for the continuous pressure decatising of fabrics. The invention also extends to a method and apparatus for continuously setting staple fibers, wherein the staple fibers are contained in an assembly of fibers such as a sliver, roving, strand, yarn or the like. The invention is particularly suitable for setting wool fibre assemblies and decatising woollen and wool containing fabrics (hereinafter the term wool fabric or the like is to be understood as encompassing fabrics containing a mixture of wool and another or other fibers) and will be described hereinafter with reference to such fibers and fabrics, but it is to be understood that the invention is applicable to other staple fibers, and to other fabrics such as, for example, cottons and rayons which are generally decatised to set the material, enhance lustre or impart some dimensional stability.
Pressure decatising is a finishing treatment whereby a wool fabric""s physical and dimensional form is enhanced and then stabilised by the use of heat, moisture, pressure and time. Generally, a pressure decatising method produces a permanent change in fabric properties by the action of heat and pressurised steam at greater than 100 kPa (1 atm) pressure on a mechanically constrained fabric, and is usually performed during the final stages of fabric production for several reasons:
(a) to develop desirable aesthetic qualities in the fabric such as handle, lustre and smoothness,
(b) to improve the dimensional stability of the fabric particularly for purposes of garment assembly, and
(c) to permanently set or preserve these qualities during fabric use. A continuous pressure decatising method imparts a permanent finish to a fabric in two distinct operations, fabric relaxation/setting followed by fabric stabilisation, For fabric relaxation/setting, the fabric is for example subjected to mechanical compression in an ambient of steam at high pressure and temperature, which allows the fibers to relax and adopt a new conformation. For fabric stabilisation, the fabric undergoes cooling and drying processes which set the fabric in its new conformation and also bring it back to room ambient. Similarly, individual fibers in an assembly of staple fibers can be treated by heat and pressurised steam whilst mechanically constrained, and then be cooled and dried to set them.
One known type of continuous decatising apparatus comprises a perforated heated drum having an endless belt held in tension and wrapped around most of the circumference of the drum. The fabric, which it conveyed between the surface of the drum and the belt as the drum rotates, is thus pressed between the drum and the belt surface. Besides being heated by the drum, the fabric is also subjected to steam which is introduced through the drum perforations. Alternatively a laminar-shaped enclosure may be formed between an impermeable pressure belt and an unperforated drum. Pressurised steam is generated in this enclosure by vaporisation of moisture carried in by the belt-fabric sandwich. The xe2x80x9cSuper finish-GFPxe2x80x9d machine made by Menschner (now MTECH) provides an example of this latter apparatus.
The pressure belt in this known type of apparatus simultaneously compresses and seals the fabric against the rotating drum. However the level of permanent set that can be imparted to the fabric is limited by the tensile strength of the pressure belt because it is the tension in this belt that provides the seal to maintain a saturated atmosphere within the fabric to set the fibers. Furthermore, the belts in this apparatus wear quickly and require frequent periodic and thus costly maintenance because of their continuously high tensile stress and high temperature working conditions. A further problem with this apparatus arises from the dual role of the pressure belt, that is, it must simultaneously form a high pressure seal with the drum and also apply mechanical pressure to the fabric. To make a leak-tight seal with the drum, the sealing pressure exerted by the belt must exceed the pressure of the enclosed steam, but the mechanical pressure actually applied to the fabric will be reduced by the xe2x80x9ccushioningxe2x80x9d effect of this steam. Consequently it is difficult to control the fabric compression as it will depend on the steam pressure within the enclosure.
Another known type of continuous pressure decatising apparatus, of which the xe2x80x9cEkofastxe2x80x9d machine developed by WIRA (Wool Industries Research Association) and Mather and Platt provides an example, involves transporting the fabric between two end less belt conveyors through an autoclave containing saturated steam. At least one of the conveyors is permeable and the fabric is subjected to impulsive compression by nip rollers. The belt conveyors in this apparatus are tensioned to maintain a desirable fabric finish. Although this tensioning is not as high as in the first described known apparatus, the belts have to be permeable and belt wear is still a problem. This apparatus can impart a reasonable permanent finish to wool fabric, however the required treatment time is much longer than that in the first described known apparatus.
Generally, known continuous pressure decatising apparatus require complex sealing arrangements due to the need to seal an enclosure of saturated steam at high pressure and yet allow a fabric to enter the enclosure, flat set and emerge from the apparatus in a continuous fashion. Example disclosures which deal With this sealing problem for continuous decasting apparatus are provided by European Patent 0533295 and International Application No. PCT/IT92/00114 (WO94/10367). A further problem is the need to ensure adequate insulation of the enclosures of saturated steam.
In summary, known continuous pressure decatising methods and apparatus involve problems with belt wear, the sealing of enclosures for saturated steam and insulating those enclosures. The solutions to these problems offered to date tend to be complex and thus costly. Furthermore, it has been difficult to date to closely control and readily adjust the steaming conditions, namely the temperature of the saturated or superheated steam to which a fabric is subjected during a continuous decatising method.
The present invention is based on the realisation that the steaming conditions in a continuous pressure decatising method may be controlled using a surrounding pressurised atmosphere, preferably of air and preferably at ambient temperature, and controlling the pressure of that atmosphere, and that such a surrounding atmosphere could also reduce the belt wear, sealing and insulation problems of the prior art. It wag also realised that this principle of using an enclosing compressed gas for controlling steaming conditions could be applied more generally for the setting of staple textile fibers as such.
Accordingly, in a first aspect of the present invention, there is provided a method for continuously pressure decatising a fabric including the steps of
(i) establishing a region of compressed gas having a pre-determined pressure,
(ii) continually conveying a fabric through the region of compressed gas by and between two conveying members,
(iii) applying saturated or Superheated steam at a high temperature to the fabric within the region of compressed gas and simultaneously pressing the fabric between the two conveying members,
wherein the high temperature of the saturated or superheated steam is determined substantially by the predetermined pressure of the region of compressed gas.
In a second aspect, the invention provides a method for setting staple fibers wherein the fibers are contained in an assembly of fibers such as a sliver, roving, strand, yarn or the like, the method including the steps of
(i) establishing a region of compressed gas having a predetermined pressure,
(ii) continually conveying the assembly of fibers through the region of compressed gas,
(iii) applying saturated or superheated steam at a high temperature to the assembly of fibers within the region of compressed gas and simultaneously constraining the fibers in the assembly of fibers,
wherein the high temperature of the saturated or superheated steam is determined substantially by the Predetermined pressure of the region of compressed gag
The method of the first and second aspects of the invention may additionally include a step of passing cool gas through the fabric, or the assembly of fibers, to cool it and reduce its regain whilst the fabric is pressed between the two conveying members, or whilst the assembly of fibers is constrained, for stabilising the fabric or the fibers. This additional step is preferably also conducted within the region of compressed gas.
According to a third aspect of the invention, there is provided apparatus for continuously pressure decatising a fabric including first and second conveying members for continuously transporting a fabric along a predetermined path, wherein each conveying member includes a facing surface and the fabric is pressed between the facing surfaces as it is transported by the first and second members along the predetermined path, wherein a treatment zone for the fabric is substantively defined by the facing surfaces of the first and second members and a portion of the length of the predetermined path; drive means associated with the first or the second member for moving said first or second member for transporting the fabric; means for providing a saturated or superheated steam atmosphere within the treatment zone; and a pressure vessel for containing a compressed gas; wherein the treatment zone is contained within the pressure vessel and wherein the pressure of the compressed gas is controllable to thereby controllably establish a high temperature for the saturated or superheated steam atmosphere within the treatment zone.
According to a fourth aspect of the invention, there in provided apparatus for setting staple fibers Wherein the fibers are contained in an assembly of fibers such as a sliver, roving, strand, yarn or the like, the apparatus including means for conveying the assembly of fibers through a treatment zone, means for constraining the fibers as they pass through the treatment zone, means for providing a saturated or superheated steam atmosphere at a high temperature within the treatment zone, and a pressure vessel for containing a pressurized gas, wherein the treatment zone is contained within the pressure vessel and wherein the pressure of the compressed gas is controllable to thereby controllably establish a high temperature for the saturated or superheated steam atmosphere within the treatment zone.
Preferably the compressed gas is air at ambient temperature. Thus, according to the invention, it is possible to change the saturated steam temperature by adjusting the pressure of the surrounding compressed air. The temperature of saturated steam at a given pressure is obtainable from Steam Tables at the equivalent vapour pressure. Also, with such a pressurised atmosphere, the sealing of the treatment zone is not critical because of the surrounding high air pressure. That is, because of the surrounding high air pressure, localized saturated (or superheated) steam is effectively maintained in the treatment zone (the degree of leakage of steam that may occur from the treatment zone is insignificant to the functioning of the decatising process). Thus the first and second conveying members may be permeable or impermeable.
The treatment zone for the fabric is generally the space between the facing surfaces of the two (or the first and second) conveying members over a length of the path of the fabric through the apparatus and there are various options available for providing a saturated or superheated steam atmosphere within this zone. At least one of the conveying members should be heated for the decatising (and thus it will have a heating arrangement associated with it) and this heating may be employed for generating the steam.
Thus a saturated or superheated steam atmosphere can be established within the treatment zone, simultaneously with the pressing and conveying of a fabric therethrough, by appropriately heating one of the conveying members such that moisture on or in the fabric is rapidly evaporated. Preferably moisture is applied to the fabric prior to its passage through the treatment zone. This can be done by spraying a surface of the fabric with moisture, which surface should be the one that faces the facing surface of the heated conveying member. Alternatively, a moisture laden textile material can be arranged to travel through the treatment zone sandwiched between the fabric being treated and the facing surface of one of the conveying members, which facing surface is suitably heated so as to rapidly evaporate the moisture that is conveyed into the treatment zone by the textile material. In this situation a permeable belt conveying member may be used in order to release excess moisture from the fabric during treatment.
In an alternative aspect, a process and apparatus according to the invention includes introducing steam into the treatment zone through the first conveying member or the second conveying member, or both, which will require that the conveying member(s) concerned be permeable. For example, one of the conveying members may be a rotatable drum and steam may be introduced into the treatment zone from inside the drum via suitable perforations through its surface. In another example, wherein the first and second conveying members comprise a permeable belt travelling over a drum, a steam chamber or the like may be provided over a portion of the belt over the drum (effectively the belt/drum interface provides a wall for the chamber). Thus in this example, pressurized steam is introduced into the treatment zone through the belt. The enclosure of such a steam chamber in a pressurized atmosphere such as compressed air, according to the invention, helps maintain the saturated steam at a temperature corresponding to this pressure and alleviates the sealing requirements for the chamber relative to the belt, thus reducing a problem which exists with prior art arrangements that employ similar steam chambers.
The first and second conveying members could be constituted by endless belt conveyors. Preferably, however, the first conveying member is a heated cylindrical drum, the outer surface of which provides one of said facing surfaces, and the second conveying member is an endless belt that travels around the drum whereby fabric, which is sandwiched between the drum and the belt, can be continuously conveyed through the apparatus via rotation of the drum. Thus, the drive means associated with the first or second member may be a driving arrangement for rotating the drum.
In this preferred drum and belt arrangement for the apparatus of the invention, the facing surface of the belt is not required to establish a seal with the facing surface of the drum along the longitudinal edges of a fabric. All that is required of the belt is that it be tensionable to exert sufficient lateral pressure to maintain a desired finish on the fabric.
In the above described preferred form of apparatus for the invention, the drum may be mounted for rotation within a pressure chamber with the belt arranged to enter and exit the chamber through suitable sealing arrangements. Compressed air at room temperature can be supplied to the chamber to maintain a suitable pressure therein while the fabric travels through. This arrangement allows for ready variation of the pressure within the chamber.
Embodiments of the invention will now be described, by way of non limiting example only, with reference to the accompanying drawings.